TEMPORAL CHANGES IN PROTEIN SYNTHESIS BY MOUSE BLASTOCYSTS TRANSFERRED TO OVARIECTOMIZED RECIPIENTS

Protein synthesis in mouse blastocysts, as inferred from the incorporation of 35S methionine in vivo, begins on day 5 of pregnancy (day 1 = the day of vaginal plug formation). The activation of protein synthesis is hormone dependent and does not occur in the absence of either estrogen or progesterone. However, previously stimulated eggs are capable of incorporating 35S methionine immediately after being transferred to ovariectomized recipients. The hormones may affect the blastocysts in two possible ways: (1) they may be responsible for the initial activation and thereafter have little or no effect; or (2) they may be necessary to both activate the blastocysts and to maintain them in an active state. To determine which of these possibilities is correct active blastocysts were recovered from intact donors on day 5 of pregnancy and transferred to the uteri of ovariectomized females. 35S methionine was given at progressively longer intervals thereafter and the blastocysts were recovered and prepared for radioautography. It was found that 35S methionine incorporation by the blastocysts decreased and finally stopped after prolonged exposure to the uteri of ovariectomized recipients. The depression was not caused by damage to the embryos; rather they simply became dormant. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company